1. Field of the Invention
This invention relates to a novel established cell line. This cell line produces a soluble factor which acts on B cells and participates in their differentiation into antibody-producing cells. These antibodies are suitable for use in the diagnosis and treatment of rheumatism, autoimmune diseases, immunodeficiency, various infectious diseases, cancer and other diseases in man and animals. These antibodies are also useful as antigens for inducing the formation of anti-idiotype anitbodies thereto. Moreover, this cell line provides a means very useful, for example, for the analysis of the mechanisms involved in the development of autoimmune diseases, immunodeficiency and the mechanisms involved in the carcinogenesis and metastasis of cancer, and the like.
2. Description of the Prior Art
In order to elucidate the pathology and etiology of autoimmune diseases or the like and make use of the results in the treatment and diagnosis thereof, and in order to analyze the mechanism of immune reactions, an increasing number of studies are being made on animals with autoimmune disease, including mouse strains with autoimmune disease (for example, lupus mouse strains such as NZB mice, NZB/W Fl mice, MRL/MP-lpr/lpr (MRL/l) mice, MRL/Mp-+/+(MRL/n) mice, BXSB mice are known). In MRL/l mice, the lymph nodes begin to swell markedly at the age of about 10 weeks, and abnormal production of autoantibodies (in particular, anti-DNA antibodies ) is observed, and lupus nephritis occurs at high rates.
As to the mechanism of antibody production, it has been elucidated that a soluble factor having the effect of inducing the differentiation of B cells is produced by T cells and takes part in the process in which the B cells having been stimulated to divide and grow and differentiate into antibody-producing cells (for example, Dutton, R. W., et al.: Prog. Immunol., 1, 355, 1971; and Schimpl, A., & Wecker, E.: Nature New Biol., 237, 15, 1972).
Such a factor is called T cell replacing factor (TRF). It is also known that this factor is produced by the mixed culture (MLR) of lymphocytes having different major histocompatibility antigens or by stimulating T cells with a mitogen such as Concanavalin A (Con A) or with non-specific antigens.
TRF is a humoral factor acting on B cells and it does not induce the proliferation of B cells, but induces the differentiation of B cells into antibody-producing cells. Accordingly, TRF is also called B cell differentiation factor (BCDF).
Conventionally known methods for the preparation of BCDF include the method of preparing BCDF by purification from the supernatant of a culture of a T cell hybridoma (Takatsu, K., et al., J. Imunol., 134, 382, 1985) and the method of producing human BCDF by use of cells derived from human B cells (Japanese Patent Laid-Open No. 169424/85).
As a differentiation factor which is produced without stimulation with a mitogen or antigen or without resorting to MLR, there has been reported one produced by T cells of the MRL/l mouse which is considered to be an animal model of human systemic lupus erythematodes (Prud'Homme, G. J., et al., J. Exp. Med., 157, 730, 1983).
Thus, the presence of various factors is known, but none of the cell lines or clones producing such factors have ever been established as cell lines having self-growing ability.
BCDF (TRF), together with anti-BCDF antibody, can be utilized in an immunoassay system for analyzing the pathological state of various diseases.
Moreover, BCDF (TRF) can also be utilized for the treatment of immunodeficiency in patients suffering from a reduction in the antibody-producing ability of B cells due to a malfunction of helper T cells.
Furthermore, a useful monoclonal antibody can be efficiently produced by culturing monocloned B cells in vitro and then stimulating their antibody production by the action of BCDF. This antibody can be utilized for the treatment and diagnosis of various diseases.
In view of the above-described usefulness of BCDF (TRF), it seems essential from an industrial point of view to obtain BCDF (TRF) in sufficient amounts, characterize it fully, and ensure industrial production thereof semipermanently. In the existing state of the art, however, BCDF-producing cell lines which have thus far been reported cannot produce BCDF stably and consistently. For example, BCDF (TRF) has neither been purified, identified or characterized fully, nor produced industrially, because no cell line of T cells capable of producing BCDF (TRF) has been established from the MRL/l mouse in the prior art.
Accordingly, it is of urgent necessity to establish a cell line which can produce BCDF (TRF) and can be stably subcultured for a long period of time.